that it paralyses every effort to prove one line of action better than another.
It was inevitable that such a self-refutation of rationality should be followed by a great outburst of
irrational faith. The quarrel between Hume and Rousseau is symbolic: Rousseau was mad but
influential, Hume was sane but had no followers. Subsequent British empiricists rejected his
scepticism without refuting it; Rousseau and his followers agreed with Hume that no belief is
based on reason, but thought the heart superior to reason, and allowed it to lead them to
convictions very different from those that Hume retained in practice. German philosophers, from
Kant to Hegel, had not assimilated Hume's arguments. I say this deliberately, in spite of the belief
which many philosophers share with Kant, that his Critique of Pure Reason answered Hume. In
fact, these philosophers--at least Kant and Hegel--represent a pre-Humian type of rationalism, and
can be refuted by Humian arguments. The philosophers who cannot be refuted in this way are
those who do not pretend to be rational, such as Rousseau, Schopenhauer, and Nietzsche. The
growth of unreason throughout the nineteenth century and what has passed of the twentieth is a
natural sequel to Hume's destruction of empiricism.
It is therefore important to discover whether there is any answer to Hume within the framework of
a philosophy that is wholly or mainly empirical. If not, there is no intellectual difference between
sanity and insanity. The lunatic who believes that he is a poached egg is to be condemned solely
on the ground that he is in a minority, or rather--since we must not assume democracy--on the
ground that the government does not agree with him. This is a desperate point of view, and it must
be hoped that there is some way of escaping from it.
Hume's scepticism rests entirely upon his rejection of the principle of induction. The principle of
induction, as applied to causation, says that, if A has been found very often accompanied or
followed by B, and no instance is known of A not being accompanied or followed by B, then it is
probable that on the next occasion on which A is observed it will be accompanied or followed by
B. If the principle is to be adequate, a sufficient number of instances must make the probability
not far short of certainty. If this principle, or any other from which it can be deduced, is true, then
the causal inferences which
-673-Hume rejects are valid, not indeed as giving certainty, but as giving a sufficient probability for
practical purposes. If this principle is not true, every attempt to arrive at general scientific laws
from particular observations is fallacious, and Hume's scepticism is inescapable for an empiricist.
The principle itself cannot, of course, without circularity, be inferred from observed uniformities,
since it is required to justify any such inference. It must therefore be, or be deduced from, an
independent principle not based upon experience. To this extent, Hume has proved that pure
empiricism is not a sufficient basis for science. But if this one principle is admitted, everything
else can proceed in accordance with the theory that all our knowledge is based on experience. It
must be granted that this is a serious departure from pure empiricism, and that those who are not
empiricists may ask why, if one departure is allowed, others are to be forbidden. These, however,
are questions not directly raised by Hume's arguments. What these arguments prove--and I do not
think the proof can be controverted--is that induction is an independent logical principle,
incapable of being inferred either from experience or from other logical principles, and that
without this principle science is impossible.